The present invention relates to calculating a downhole temperature in a hydrocarbon well installation.
The safe and efficient operation of an offshore oil or gas well relies on a knowledge of the reservoir characteristics and the ability to control the flow of fluid from the well. This requires knowledge of the temperatures and pressures at various positions downhole in the well, which enables an operator to control more efficiently, the flow of fluid or gas from the well, and enables reservoir engineers to develop a model or simulation of the reservoir and calculate reserves, etc. The temperature of the reservoir fluid entering the well is also an important measurement, as it allows the operator to detect water or gas breakthrough.
Although the downhole technology is now becoming available for measuring fluid flow, temperature and pressure measurements in offshore oil and gas wells is proving to have poor reliability when operating in the harsh downhole environments of existing wells. With the move to deeper water wells with their harsher downhole environments and higher temperatures (up to 200 degrees C.) and pressures (up to 1000 bar) there is a need to improve measurement reliability. The current sensor technology, providing the required accuracy and resolution, is based on quartz crystals which can survive the harsh environments, but the associated downhole electronics, cables, connectors and communication system that all have poor mean time between failures, in the downhole environment.
Current downhole instrumentation, therefore, does not provide the necessary reliability required for the safe and efficient operation of offshore deepwater wells and there is a need to improve the reliability of downhole temperature and pressure measurements.
The difficulty of using electronics based sensors downhole can be avoided by using distributed fibre-optic sensing techniques which have the intrinsic capability of being more reliable than traditional sensing, in that no downhole electronic equipment is required. However, this technology is currently at an early stage in its operational lifecycle. In any event, using sensors mounted on a Christmas tree located on the seabed, to provide estimates of downhole temperatures and pressures, will provide an essential back-up in the event of failure, for example, of the fibre-optic cable.